Avid Aviator - I don't have the regs with me right now to quote but careful reading of them will tell you that it is NOT an unequivocal requirement that the BFR MUST be done in the aircraft that the individual has flown most over the last 10hrs or so. From memory there is some reference to category (eg plane, chopper, airship) that needs to be considered - there is room to move within those categories.